Drill or milling head

ABSTRACT

A drilling or milling head, especially for printed circuit board milling machines and/or engraving machines, having a collet chuck ( 11 ) which can be actuated by a rapid change mechanism and which is driven by a transmission. The collet chuck is opened by an axial displacement relative to a clamping sleeve ( 50 ), with the force necessary for the displacement being transmitted via a friction clutch. The transmission includes a ball bearing ( 9 ) whose balls ( 12 ) are moved around a common axis in a concentric manner by a driving part ( 6 ) fixed on a motor drive shaft ( 5 ). In addition, the balls are mounted between two bearing surfaces ( 13, 14 ) which are aligned in a concentric manner with regard to the axis and which have a circular cross-section. The balls are at least partially engaged with the bearing surfaces in a positive manner. The bearing surfaces, one of which can rotate and the other of which is fixed, are axially aligned and symmetrical to one another, and they are concavely curved with the maximum distance between the convex surfaces being equal to the ball diameter. The balls are subjected to an axial force. The drilling or milling head of the invention makes it possible to drive the collet chuck at a different speed than that of the motor.

BACKGROUND OF THE INVENTION

This invention relates to a drilling or milling head with a collet chuckoperated by a quick-change mechanism and a drive shaft connected to amotor, the collet chuck being opened by axial displacement with respectto a clamping sleeve and the force necessary therefor being transferredthrough a friction clutch, and having a transmission for driving thecollet chuck. In particular, this drill or milling head is suitable formachines which serve for the production of fine structures such ascircuit-board milling machines and engraving machines.

In the as yet unpublished patent application Ser. No. 197 48 735.1 adrilling or milling head of this kind is described. In this drilling ormilling head a drive shaft of the motor is connected by a coupling to adrive shaft of the collet chuck. Thus, the rotatory speed of the chuckedtool is always equal to the motor speed.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to provide a drilling ormilling head of this kind in which the rotation of the motor drive shaftcan be transferred with a gear ratio to the drive shaft of the drillingor milling head by means of a transmission based on simple means.

This object is achieved by the invention as described and claimedhereinafter. In the drilling or milling head according to the invention,the driving part of the transmission is a ball bearing whose balls aredriven concentrically about a common axis by means of a driving partfastened on a drive shaft of the motor. The balls are mounted betweentwo bearing surfaces of circular cross section aligned concentricallywith the axis, and engaged in an at least partially force-transmittingmanner with them. One of the bearing surfaces is rotatable about theaxis while the other bearing surface remains fixed. Also, the bearingsurfaces are aligned substantially parallel to the axis and concavelycurved in the axial direction symmetrically to one another, the maximumdistance of the curves from one another being approximately equal to thediameter of the balls. A force is applied axially to the balls by thedriving part.

The transmission is based on the principle that the balls movesimultaneously relative to two concentric circumferential surfacesserving as bearing surfaces, which are circular in cross section andhave different radiuses. The result is different angular velocities ofthe motor drive shaft and the driven bearing surface, corresponding tothe ratio of the radiuses of the bearing surfaces.

Thus a drilling or milling head is provided with a transmission that isspace-saving and subjected hardly at all to wear. Since it is based onsimple means, the transmission can also be manufactured at low cost.Since the bearing surfaces are aligned substantially parallel to theaxis and concavely curved in the axial direction, and indeed such thatthe curvatures are symmetrical with one another, i.e., with respect tothe axis passing through the balls about which the balls rotate, andfurthermore since the balls are subjected to a force by the drivingpart, the balls are urged against an area of the curves in which thedistance of the curves from one another is less than the diameter of theballs. In this manner a force-transmitting engagement of the balls withthe bearing surfaces is achieved, resulting in a simple form of aslipping coupling.

Inasmuch as the bearing surfaces are concavely curved, the axial travelof the driving part is especially short—shorter, for example, than inthe case of the surfaces tapering in the axial direction. Due to thecurvature of the bearing surfaces the balls come very quickly intoengagement with the bearing surfaces.

The driving part can be biased by a spring which is fastened on themotor drive shaft between a motor housing and the driving part. Thespring absorbs the reaction force upon engagement and simultaneouslyoffers protection against overload due to excessive heating of the ballsand the races. The spring force is to be adjusted accordingly when thetransmission is assembled.

The transmission can be used both for increasing speed and for reducingspeed. To achieve a speed increase, the bearing surface having thegreater radius is fixed. In this manner the part that forms the bearingsurface having the smaller radius is caused to rotate. This part candirectly be a section of the drive shaft of the drilling and millinghead, or it can also be joined to this drive shaft through a coupling.

The bearing surfaces can be formed by a bearing inner ring or a bearingouter ring. The bearing outer ring, if it is fixed, can be inserted in ahousing of the transmission. The bearing inner ring can be pressed onthe driven part.

Preferably the driving part fastened on the motor drive shaft is atoothed flange whose teeth are engaged between the balls. Provision canbe made for pressing seats in the axial direction into the toothedflange for the balls of the ball bearing. The toothed flange ispreferably made from wear-resistant material. Sintered bronze,preferably impregnated with oil, is especially suited to the purpose.

The friction clutch of the drilling or milling head preferably iscomprised of a part that can be moved axially and relative to the driveshaft of the drilling or milling head and a part that is axiallydisplaceable and affixed to the drive shaft of the drilling or millinghead, the two parts having faces which conform to one another which comein contact when the quick change mechanism is operated. Provision ismade for the two parts each to be supported on the tool side against theforce of a spring. This assures that in a state of rest, the two partswill be spaced a distance from one another, and in case the part of thedrilling or milling head affixed to the drive shaft rotates onlyfriction will occur between the surfaces, which does not result indamage to the drilling or milling head.

According to a preferred embodiment of the drilling or milling head, thepart that can be moved relative to the drive shaft of the drilling ormilling head is cylindrical and is arranged concentrically with thisdrive shaft, and has on the end toward the motor an annular shoulder.The part of the drilling or milling head that is affixed to the driveshaft is a sleeve with a circumferential flange. The conforming surfacesare formed on the annular shoulder and on the circumferential flangeplanar and perpendicular to the shaft.

Since the force necessary for the axial shifting of the collet chuck istransmitted by a friction clutch, it is impossible for an accidentallystill rotating collet chuck when opened to come into locking engagementwith a non-rotating part. The axial displacement force is insteadtransferred in a positive manner through the friction clutch to thecollet chuck, or to the drive shaft to which the collet chuck isattached.

The quick change mechanism can be operated manually through a handactuator. Provision can also be made for the hand actuator to be lockedin the position in which the collet chuck is open. This has theadvantage that the operator has both hands free to manipulate thedrilling or milling tool.

The hand actuator can be, for example, a lever which has a handlesection and a functional section disposed within a housing of thedrilling or milling head. It is anticipated that in the rest positionthis functional section of the lever will form an inclined angle to ahorizontal plane and in the actuated position it will assume a rightangle to the drive shaft of the drilling or milling head, andfurthermore lies against an immovable surface of the drilling or millinghead and, on the tool side, against the part that is movable relative tothe drive shaft. When in the actuated position the functional section ofthe lever has a greater maximum length in the axial direction than inthe rest position. Thus, moving the lever from its rest position to itsactive position causes the part of the friction coupling that can moverelative to the drive shaft to be displaced toward the tool end of thedrilling or milling head, and at the same time, as will be describedbelow, the drive shaft and collet chuck are also displaced so as tocause the collet chuck to open.

The functional section of the lever is preferably annular and arrangedconcentric to the drive shaft. If the outside diameter of the functionalsection is equal to the inside diameter of the housing and the outsideof the functional section is convexly curved, to outside of thefunctional section will be in contact with the housing of the drillingor milling head in any position along its entire circumference, exceptfor an area in which the handle section is attached. This assures thatthe lever only changes its angular position relative to the drive shaftand optionally can be rotated slightly about the axis of the drilling ormilling head to lock it in position, but beyond that it is fixed. Thehandle extends through an opening in the housing.

The maximum extension of the functional section in the axial direction,which is variable according to its position, is preferably achieved inthat on the functional section of the lever, cams are disposed on thetool side on both sides of the drive shaft in the plane perpendicular tothe longitudinal axis of the lever in which the drive shaft lies whenthe lever is in the actuated position, and an additional cam is disposedon the motor side opposite the handle part of the lever. The two cams onthe tool side and the cam on the motor side are thus offset by 90°.Therefore the functional section, when in the horizontal position, i.e.,in the actuated position, has a greater axial length than in theinclined or rest position.

When the lever is moved from its rest position to its actuated position,the two cams on the tool side press against an abutment surface of thepart that is movable in the axial direction relative to the drive shaft.This latter part then moves toward the collar affixed to the driveshaft. Thus, by actuating the lever, the drive shaft is shifted towardthe tool end of the drilling or milling head. With the drive shaft, thecollet chuck is also displaced relative to the clamping sleeve. Thisopens the chuck whose gripping jaws lie in contact in the end section ofthe clamping sleeve with an inner surface of the clamping sleeve whichconically converges in the axial direction toward the motor.

The quick change mechanism can also be operated pneumatically.

In order to permit an easy separation of the motor and drilling ormilling head, the transmission and the drive shaft of the drilling ormilling head can be connected together with a coupling. This coupling ispreferably a resilient coupling so as to enable vibrations in the axialdirection to be absorbed.

If need be, the drilling or milling head can be connected very easily bythe coupling to different motors. The result is a modular constructionof a drilling or milling head which is a completely independent unitwith the mechanism for a quick and reliable tool change.

It can also be arranged according to the invention for two or moreoperatively connected transmissions of the kind described to be arrangedone after the other. The driven part of the first drive then engagesbetween the balls of the second transmission. In this manner, forexample, the rotatory speed of the drive shaft of the drilling ormilling head can be further increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The drilling or milling head according to the invention will be furtherexplained below with respect to a working embodiment, reference beingmade to the drawings, in which:

FIG. 1 is a sectional view of a drilling or milling head.

FIG. 2 is a detail view of the transmission of the drilling or millinghead of FIG. 1.

FIG. 3 is an enlarged view of the mounting of one of the balls of theball bearing.

FIG. 4 is a plan view of a toothed flange.

FIG. 5 is a sectional view of the toothed flange of FIG. 4.

FIG. 6 is a perspective view of the toothed flange of FIGS. 4 and 5.

FIG. 7 shows the principle of increasing the speed by means of thetransmission.

FIG. 8 is a sectional view of the housing of the drilling or millinghead, which has a locking device for a handle of the quick-changemechanism.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The drilling or milling head 1 shown in FIG. 1 has a housing 2 which isconnected by two screws 3 and 3′ with a motor 4, which is indicated onlyschematically. The motor 4 has a drive shaft 5.

A toothed flange 6 made of oil-impregnated sintered bronze is fastenedby means of a pin 7 on the drive shaft 5. The teeth 8 and 8′ of thetoothed flange 6 extend into a ball bearing 9. The ball bearing 9 isarranged between the housing 2 of the drilling or milling head 1 and thedriven part 10 of the driving mechanism. The driven part 10 drives acollet chuck 11 through a drive shaft 31 of the drilling or milling head1. Before this drive mechanism is described, first the transmission willbe explained in detail.

As shown in detail in FIG. 2, the balls 12 and 12′ of the ball bearing 9are held between an inner bearing surface 13 and an outer bearingsurface 14. The inner bearing surface 13 is formed by a inner bearingring 15, and the outer bearing surface 14 by an outer bearing ring 16.The inner bearing ring is pressed onto the driven part 10 of the drivingmechanism. The outer bearing ring 16 is inserted in the housing 2 of thedrilling or milling head 1.

Between the toothed flange 6 and the motor 4 a spring 17 is arrangedwhich exerts an axial force against the toothed flange 6.

The inner bearing surface 13 and the outer bearing surface 14 are shownenlarged in FIG. 3 together with one ball 12 of the ball bearing 9. Thetwo bearing surfaces 13 and 14 have each a concave curvature 18 and 19,respectively. The curves 18 and 19 extend axially over a length that isslightly greater than the diameter of the ball 12. The two curves 18 and19 are configured symmetrically to one another with respect to the axis20 passing through the ball 12. The maximum distance between the curves18 and 19 is equal to the diameter of the ball 12. This distance isbetween the centers of the curves 18 and 19.

An axial force which is indicated by the arrow 21 is exerted on the ball12 by the toothed flange 6 (not shown in FIG. 3). Depending on theexerted force 21, the ball 12 assumes different axially displacedpositions 22 or 23, respectively, which are represented in FIG. 3 by asolid line 22 and a broken line 23, respectively.

In FIGS. 4, 5 and 6 the structure of the toothed flange 6 is shown indetail. The toothed flange 6 has a bore 24 in which the drive shaft 6 ofthe motor is engaged. The toothed flange 6 is fastened on the driveshaft 5 by the pin 7 that is perpendicular to the drive shaft 5. Thetoothed flange 6 has a circular cross section, with six teeth 8 arrangedon its circumference. Between the teeth 8 are seats 12 a for the balls12. The seats 12 a are pressed axially into toothed flange 6 and have adepth of about 0.2 mm and a diameter of about 1.5 mm.

In FIG. 7 the principle of operation of the driving mechanism is furtherexplained, in particular for the case of a rotary speed increase. Theball 12 is rotated by the toothed flange 6 (not shown in FIG. 6) in thedirection of arrow 25. The ball 12 thus runs on the outer bearingsurface 14 which is formed by the fixed outer bearing race 16. The innerbearing race 15, in contrast, is rotatably mounted. Due to theself-rotation of the ball 12 indicated by the arrow 26 and a drivingengagement of the ball 12 with the bearing's inner ring 15, the innerring 15 rotates in the direction of the arrow 27. The angular velocityof the rotation of ball 12 on the axis 28 is equal to the angularvelocity of the toothed flange 6 and drive shaft 5 of the motor 4. Theangular velocity of the inner bearing ring 15, however, is greater,namely by a factor that is equal to the ratio of the radius of the outerbearing ring 16 to the radius of the inner bearing ring 15.

The driving engagement of ball 12 with bearing surfaces 13 and 14 isbrought about by the axial force 21 which is exerted by the motor 4 andthe spring 17 on the toothed flange 6, which in turn presses against theballs 12 of the ball bearing 9. Thus the air gap 29 (see FIG. 2) isaccordingly reduced. Due to the driving engagement the balls 12 rotate,as a rule accompanied by the occurrence of an initial slippage, bothabout their own axes and about the axis of the driven part 10 of thedriving mechanism. The inner bearing race 15 is thus also rotated, andsince it is affixed to the driven part 10 of the transmission, thedriven part 10 also is rotated.

Because of the ball seat 12 a no readjustment of the spring 17 isnecessary during operation.

With the driving mechanism it is thus possible to achieve a speedincrease in a simple manner. It is also possible, however, to use thedriving mechanism in a reverse manner for a reduction of speed. In sucha case the inner bearing race 15 must be fixed while the outer bearingrace 16 must be mounted for rotation.

The drive mechanism for the drilling or milling head 1 is describedhereinafter, and also a mechanism for a rapid and safe tool change.

The driven part 10 of the driving mechanism contains an elastic couplingdisk 30. The coupling disk 30 is opposite a plate-like attachment 32which is fastened on the drive shaft 31 of the drilling or milling head1, and which forms together with the driven part 10 of the transmissionand two connecting pins 33 and 34 a coupling between the driven part 10of the transmission and the drive shaft 31 of the drilling or millinghead 1. The connecting pins 33 and 34 are fixed in the attachment 32 onthe drive shaft 31 of the drilling or milling head 1 and engage inrecesses in the coupling disk 30.

The drilling or milling head furthermore has a lever 37 with afunctional section 38 disposed within the housing 2 and a handle 38projecting out of the housing 2. The functional section 38 is annularand concentric with the drive shaft 31 of the drilling and milling head1. The functional section 38 has such a diameter and is convexly curvedon the outer surface such that, in every position, except for a range inwhich the handle section 39 is attached, it is in contact with thehousing 2 of the drilling and milling head 1. On the side of thefunctional section 38 facing the motor 4 a cam 40 is disposed. On theopposite side of the functional section 38 two cams 41 are disposed,only one of which is shown. These two cams 41 lie in the plane rotated90° around the drive shaft 31 from the section plane. On the motor sidethe function section 38 is in contact with a fixed ring 42, and on thetool side it is in contact with a cylindrical part 43 which is movablein the axial direction and which in turn is supported on the tool sideby a spring 44 against a projection 45 of the housing 2. On the endtoward the motor 4 this part 43 has an annular shoulder 46 which is at aright angle to the wall of part 43.

A collar 47 with a circumferential flange 48 is affixed to the driveshaft 31. The flange 48 is aligned parallel with the shoulder 46 and ofsuch dimensions that, upon a movement of part 43 toward the tool end ofthe drilling and milling head 1, the confronting planar surfaces of theshoulder 46 and flange 48 come in contact. On the tool side, the collar47 is supported by a spring 49 against a clamping sleeve 50. Theclamping sleeve 50 surrounds a section of the drive shaft 31 and, exceptfor a short end portion, it surrounds the entire collet chuck 11 withwhich the drive shaft 31 merges. A pin 51 passing transversely throughthe drive shaft 31 extends on both sides of the drive shaft 31 intoelongated slots 52 and 53 each running parallel to the drive shaft 31 inthe clamping sleeve 50.

The clamping sleeve 50 is journaled on two bearings 54 and 55 andsecured by a snap ring 56 against axial displacement. The clampingsleeve 50 has in its end section an interior surface 57 which convergesconically in the axial direction toward the motor 4. The gripping jaws58 of the collet chuck 11 are in contact with this interior surface 57when the collet chuck 11 is closed.

As shown in FIG. 8, in this embodiment provision is made for locking thelever 37 in its actuated position, i.e., in the open state of the chuck11. For this purpose an opening 59 of substantially right-angle shape isprovided in the housing 2 for the lever 37, one leg 60 thereof beingaligned axially. The second leg 61, which at its outer end has a recess62 extending in the same direction as leg 60, forms a catch for thelever 37.

When a tool (not shown) is clamped in the drilling and milling head 1,the lever 37 is in its rest position shown in FIG. 1. It is held in thisposition, in which the functional section 38 of lever 37 has its leastaxial elongation, by the force of spring 44 transmitted throughcylindrical portion 43. If the lever 37 is moved to its horizontalposition, the axial elongation of functional section 38 increases sothat the moving part 43 is shifted toward the tool end of the drillingand milling head 1. In this way the two confronting planar faces of theshoulder 46 and flange 48 are brought into contact, so that the collar47 is also displaced. Since the collar 47 is affixed to the drive shaft31, the drive shaft 31 and the chuck 11, which directly adjoins thedrive shaft 31, move toward the tool end of the drilling and millinghead 1. As a result of the displacement of the collet chuck 11 withrespect to the clamping sleeve 50 which is fixed in the axial direction,the gripping engagement of the conical inner surface 57, the clampingsleeve 50 and the gripping jaws 58 of the collet chuck 11 is relaxed, sothat the tool held by the gripping jaws 58 is released.

The pin 51 and the elongated slots 52 and 53 constitute an interlock bymeans of which the clamping sleeve 50 always will rotate with the driveshaft 31, so that no friction occurs between these two parts. The slots52 and 53 assure that the drive shaft 31 can thereby shift axially withrespect to the clamping sleeve 50.

When lever 37 is moved to its actuating position, the connecting pins 33and 34 of the coupling between the driven part 10 of the transmissionand the drive shaft 31 also move toward the tool end of the drilling andmilling head 1. However, they do not pass entirely out of their recesses35 and 36, so that disengagement does not occur.

To lock the lever 37, it is rotated in its actuated position slightlyaround the axis of the drilling and milling head 1, so that it isreceived and held in the recess 62.

If the motor 4 is accidentally left on before the lever 37 is operated,nevertheless no damage can be done to the drilling and milling head 1and there is no danger of injuring persons, since the contact surfacesof the cylindrical part 43 and the collar 47 are designed to withstandthe resulting friction heat and the collet chuck 11 cannot come loosefrom the drive shaft 31.

What is claimed is:
 1. A drilling or milling head comprising: a housing;a rotatable collet chuck which is opened by axial displacement withrespect to a clamping sleeve mounted within said housing; a drive shaftoperatively connected to a motor for rotatably driving the collet chuck;a transmission interposed between the motor and said drive shaft forstepping up or stepping down the rotational speed of said collet chuckrelative to said motor; and a quick change mechanism for opening saidcollet chuck, said quick change mechanism including a friction clutchthrough which force required to axially displace and open said colletchuck is transferred to said collet chuck; wherein said transmissioncomprises outer and inner bearing rings disposed concentrically aroundan axis of said drilling or milling head and having respective opposedbearing surfaces which are concavely curved in the axial direction andwhich are symmetrical to each other, one of said outer and inner bearingrings being fixed relative to said housing and the other of said outerand inner bearing rings being mounted for rotation about said axis andcoupled to said drive shaft, a plurality of balls disposed between thecurved bearing faces of said outer and inner bearing rings, the maximumspacing of said curved bearing faces from each other being equal to thediameter of said balls, and a driving part rotated by the motor fordriving said balls around said axis along the curved bearing surface ofthe fixed bearing ring, said driving part exerting an axial forceagainst said balls to urge said balls into force-transmitting engagementwith said bearing surfaces, whereby the rotationally mounted bearingring and the drive shaft are caused to rotate.
 2. A drilling or millinghead according to claim 1, further comprising a spring arranged betweenthe motor and the driving part for biasing the driving part against saidballs.
 3. A drilling or milling head according to claim 1, wherein thefixed bearing ring has a larger radius than the rotatably mountedbearing ring.
 4. A drilling or milling head according to claim 1,wherein said bearing surfaces are formed, respectively, by an innerbearing race and an outer bearing race.
 5. A drilling or milling headaccording to claim 4, wherein the outer bearing race is inserted in ahousing of the drilling or milling head.
 6. A drilling or milling headaccording to claim 4, wherein the inner bearing race is pressed onto adriven part coupled to said drive shaft.
 7. A drilling or milling headaccording to claim 1, wherein said driving part comprises a toothedflange with teeth which extend between said balls.
 8. A drilling ormilling head according to claim 7, wherein said toothed flange isprovided with axially recessed seats for said balls.
 9. A drilling ormilling head according to claim 1, wherein said driving part is madefrom oil-impregnated sintered bronze.
 10. A drilling or milling headaccording to claim 1, wherein the friction clutch comprises an axiallymovable part movable axially and relative to the drive shaft of thedrilling or milling head and an axially displaceable part affixed to thedrive shaft, said movable part and said displaceable part each beingsupported by a respective spring and both having conforming surfaceswhich come in contact with each other when said quick release mechanismis actuated.
 11. A drilling or milling head according to claim 10,wherein said movable part relative to the drive shaft is cylindrical andis disposed concentrically with the drive shaft and has an annularshoulder on one end toward the motor, and wherein said displaceable partaffixed to the drive shaft comprises a collar with a circumferentialflange, and said conforming surfaces are flat and extend perpendicularto the drive shaft.
 12. A drilling or milling head according to claim 1,wherein the quick change mechanism is provided with an operating handlefor operating the quick change mechanism.
 13. A drilling or milling headaccording to claim 1, wherein said quick change mechanism ispneumatically operated.
 14. A drilling or milling head according toclaim 1, further comprising a resilient coupling disk for connecting thesaid drive shaft of the drilling or milling head to the motor such thatthe drilling or milling head and the quick change mechanism togetherform an independent unit.
 15. A drilling or milling head according toclaim 14, wherein said resilient coupling disk is arranged toselectively connect the drilling or milling head with different motors.